An engine's powertrain control module may be configured to compute a desired throttle position based on engine operating conditions and a throttle position may be accordingly adjusted. By adjusting the throttle position, an actual intake airflow rate may be shifted towards a commanded airflow rate. The commanded throttle position, and hence the commanded airflow rate, may be adjusted to compensate for demands on the intake manifold vacuum by vacuum-based actuators, such as a vehicle brake booster.
One example approach for throttle control in view of brake booster vacuum demand is shown by Cunningham et al. in US 2011/0183812. Therein, a throttle position is adjusted in response to a rate of air flowing from the brake booster to the intake manifold so as to maintain intake manifold pressure substantially constant. For example, the throttle is closed when the brake booster is replenished with vacuum from the intake manifold.
However, the inventors herein have recognized potential issues with such an approach.
As an example, by adjusting the throttle position to achieve a desired instantaneous airflow rate in the intake manifold, an average desired airflow rate may be affected. Specifically, even though the instantaneous airflow rate (after clipping for minimum effective area constraint) is achieved, and the commanded throttle position is achieved, substantial errors may be incurred between the average actual airflow rate and the airflow rate that would be commanded if a minimum effective throttle area constraint was not encountered. As a result, engine air amount disturbances (e.g., un-throttled air flow) may be generated as air is exchanged from the brake booster to the engine intake manifold.
As another example, during brake pedal application, negative throttle angles may be required to reduce the manifold pressure variation. Since negative angles are not possible due to physical limits of the throttle, in Cunningham et al., the throttle is maintained closed as long as the negative throttle angle is commanded. Then, when the brake pedal is released and an increase in throttle angle is commanded, the throttle is moved to the commanded position. However, due to the negative throttle angle not being achieved, throttle angle errors may persist, which in turn may lead to substantial engine air amount errors. The engine air amount disturbances can increase engine emissions and may be noticeable to the driver. Additionally, the achieved intake manifold vacuum is not as low for as long as it would have been if the average air flow rate were achieved.
In one example, some of the above issues may be at least partly addressed by an engine method comprising, adjusting a signal indicative of a commanded throttle position with a correction based on an integrated airflow rate error. Then, the throttle may be actuated to the adjusted throttle position. In this way, integrated throttle angle errors and airflow rate errors may be reduced.
For example, while an engine is operating, a controller may continuously modify a commanded throttle position with a correction term (e.g., an adder) that is based on an error between an actual throttle airflow rate (or actual throttle position/angle) and the commanded throttle airflow rate (or commanded throttle position/angle). In addition, the correction term may be continuously updated based on the feedback data. In this way, the error may be substantially reduced towards zero, and on average, the actual throttle position may converge to the unclipped commanded throttle position.
In addition, during pedal transients (such as, during a brake pedal transient), the throttle position may be adjusted with the correction to reduce the integrated error. For example, if a negative throttle angle is commanded, the throttle may be closed as long as the negative throttle angle command persists. Then, when an increase in throttle angle is subsequently commanded, the throttle angle may be intentionally increased at a slower rate than desired. By slowing the rate of throttle angle increase, a throttle angle error incurred while the negative throttle angle was commanded (but not provided) may be compensated for. In this way, throttle airflow rate errors and throttle angle errors may be reduced. By substantially eliminating throttle airflow rate errors, engine air disturbances may be reduced. Overall, engine performance and emissions may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.